(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to an LCD in which a predetermined opening pattern is formed at pixel and common electrodes such that a wide viewing angle is obtained.
(b) Description of the Related Art
Generally, an LCD has a structure having a liquid crystal layer that is sandwiched between two substrates. An electric field is applied to the liquid crystal layer to control the alignment of the liquid crystal molecules, ultimately controlling the transmittance of incident light. In a vertically alligned (VA) LCD, the liquid crystal molecules are aligned perpendicular to the substrates when an electric field is not applied. In case two polarizer films are arranged with their polarizing directions perpendicular to each other, the linearly polarized light passing through the first polarizer film is completely blocked by the second polarizer film in the absence of an electric field. The complete blockage of lights exhibits a very low brightness in an xe2x80x9coffxe2x80x9d state of the normally black mode. This helps a VA LCD obtain a relatively higher contrast ratio than that of the conventional TN liquid crystal display.
However, the liquid crystal molecules are irregularly inclined against the substrate when an electric field is applied. Therefore, in one or more areas, the long axis directions of some of the liquid crystal molecules are aligned with the polarizing direction of the first polarizer film or the second polarizer film. In such areas, the liquid crystal molecules cannot rotate the polarizing direction, i.e., polarization, and the light is completely blocked by the polarizer film. Such areas appear as black portions on the screen, which degrade the in picture quality. These areas are referred to as areas of xe2x80x9ctexture.xe2x80x9d
In order to solve the above problem, several techniques of electrode-patterning have been suggested. However, a slow response time still remains as a problem.
FIG. 1 illustrates a schematic view of opening patterns formed at pixel and common electrodes in a prior art liquid crystal display. As shown in FIG. 1, the pixel and common electrodes are formed with opening patterns 1 and 2, respectively. Each of the opening patterns 1 and 2 is formed in a V-shape and is arranged with ends of the V-shapes in proximity to each other so that roughly a diamond shape is formed by the opening patterns 1 and 2. Liquid crystal material is injected between the pixel electrode and the common electrode, and liquid crystal molecules 3 are aligned perpendicular to the electrodes.
When an electric field is applied to the liquid crystal material, the liquid crystal molecules 3 come to be arranged parallel to the electrodes. However, the response speed of the liquid crystal molecules 3 with respect to the applied electric field is very slow with the formation of the opening patterns 1 and 2 at the pixel and common electrodes. That is, as a result of a fringe field formed due to the opening patterns 1 and 2, the liquid crystal molecules 3 are first arranged perpendicular to the opening patterns 1 and 2 (A state), then are aligned to be parallel with one another (B state), because liquid crystal molecules tend to align themselves roughly parallel along their long axes. These two steps of alignment slow down the response speed.
The slow response speed of liquid crystal molecules generates after-images when displaying moving pictures on the screen. There is therefore a need to increase the response speed of liquid crystal molecules.
It is an object of the present invention to provide a liquid crystal display which has an improved response speed and a wide viewing angle.
It is another object of the present invention to provide a liquid crystal display that shows improved picture images.
These and other objects may be achieved by a liquid crystal display having a first insulating substrate with top and bottom surfaces. A pixel electrode is formed on the top surface of the first insulating substrate. The pixel electrode has a first opening pattern at each pixel area. The pixel electrode with the first opening pattern is substantially rectangular in shape and having first and second long sides, and first and second short sides. The pixel electrode is divided into an upper region defined by the first and second long sides and the first short side, and a lower region defined by the first and second long sides and the second short side. A second insulating substrate with top and bottom surfaces is arranged parallel to the first insulating substrate at a predetermined distance from the same such that the bottom surface of the second insulating substrate faces the top surface of the first insulating substrate. A common electrode is formed on the bottom surface of the second insulating substrate. The common electrode has a second opening pattern at each pixel area, which corresponds to each pixel area of the pixel electrode. A liquid crystal layer is sandwiched between the first and second substrates while contacting the pixel and common electrodes.
The first and second opening patterns each have a plurality of openings, the openings of the first and second opening patterns being alternately arranged parallel to each other.
The first and second opening patterns each have a middle linear portion. The linear portions of the first and second opening patterns are alternately arranged parallel to each other. The first opening pattern includes a first opening formed in the upper region of the pixel electrode in a first direction. A second opening portion is formed in the lower region of the pixel electrode in a second direction normal to the first direction. The second opening pattern includes a first trunk opening formed in the upper region of the common electrode in the first direction, and a second trunk opening formed in the lower region of the common electrode in the second direction. The first direction is slanted at a predetermined angle with respect to the long or short sides of the pixel electrode. The second opening pattern further includes first branch openings overlapping the first and second short sides of the pixel electrode, and second branch openings overlapping the first and second long sides of the pixel electrode. The first opening pattern further includes a third opening formed where the upper and lower regions of the pixel electrode meet while proceeding parallel to the first and second short sides of the pixel electrode. The second branch openings each have a width greater than that of the trunk opening portion. The first direction is parallel to one of the long and short sides of the pixel electrode. The first and second trunk openings each have opposite ends respectively with a gradually enlarged width One of the second trunk openings overlaps the second short side of the pixel electrode. The first opening has opposite ends respectively with a gradually reduced width
The pixel and common electrodes are overlapped with each other such that the first and second opening patterns partition the pixel electrode into several micro-regions. The micro-regions of the pixel electrode are in the shape of polygons where the longest sides are parallel to each other. The micro-regions of the pixel electrode are classified into a first type where the longest sides are arranged in a first direction, and a second type where the longest sides are arranged in a second direction normal to the first direction. The first direction is slanted at a predetermined angle with respect to the long or short sides of the pixel electrode. Alternatively, the first direction may be parallel to one of the long and short sides of the pixel electrode.
The first and second opening patterns form fringe fields when voltage is applied between the pixel and common electrodes. The orienting direction of the liquid crystal molecules due to the fringe fields corresponds to that of the liquid crystal molecules as a result of a force exerted by the molecules. It is preferable that the liquid crystal molecules are oriented in four directions. The opening width of the first and second opening patterns is preferably in the range of 10-16 xcexcm
The pixel electrode may have protrusions at the sides adjacent to the ends of the first and second openings.